The separation of polar (or polarizable) impurities from hydrocarbons or mixtures of hydrocarbons to reduce their contents to ppm (parts per million) levels is of great technical importance but is often found to pose significant technical problems. The importance of such purification processes resides in the fact that many polarizable impurities in hydrocarbons and mixtures of hydrocarbons limit their technical usefulness because the impurities have either disturbing effects on the actual technical process using the hydrocarbon or because they result in the formation of by-products, which are undesirable from an environmental point of view. Important examples thereof include the separation of sulfur and nitrogen components from fuels for reducing the SO2 emissions or the reduction of chlorine-containing compounds from motor oils to avoid corrosion problems.
The deep desulfurization of fuels to achieve very low sulfur contents (>50 ppm) is a great problem in the production of fuel. Regulations currently require a reduction of the sulfur content in gasoline and diesel fuels to 50 ppm for the year 2005 within the European Union. Propositions by the German government already aim at a reduction to 10 ppm in the year 2003 (W. Bonse-Geuking, Erdöl Erdgas Kohle, 116, 9 (2000) 407). According to the current state of the art, the separation of sulfur-containing compounds is effected by catalytic hydrogenation in refineries (J. Pachano, J. Guitian, O. Rodriguez, J. H. Krasuk (Intevep, S. A.), U.S. Pat. No. 4,752,376 (1988), Jr. Hensley, L. Albert, L. M. Quick (Standard Oil Company), U.S. Pat. No. 4,212,729 (1980), S. B. Alpert, R. H. Wolk, M. C. Chervenak, G. Nongbri (Hydrocarbon Research, Inc.), U.S. Pat. No. 3,725,251 (1971), G. R. Wilson (Gulf Research & Development Company), U.S. Pat. No. 3,898,155 (1975), Y. Fukui, Y. Shiroto, M. Ando, Y. Homma (Chiyoda Chemical Engineering & Construction Co., Ltd.), U.S. Pat. No. 4,166,026 (1979), R. H. Fischer, J. Ciric, T. E. Whyte (Mobil Oil Corporation), U.S. Pat. No. 3,867,282 (1975), J. G. Gatsis (Universal Oil Products Company), U.S. Pat. No. 3,859,199 (1975), L. K. Riley, W. H. Sawyer (Esso Research and Engineering Company), U.S. Pat. No. 3,770,617 (1973), C. E. Adams, W. T. House (Esso Research and Engineering Company), U.S. Pat. No. 3,668,116 (1972)). The separation of the hydrogen sulfide formed is effected by amine washers (W. W. Kensell, M. P. Quinlan, The M. W. Kellogg Company Refinery Sulfur Management, in: R. A. Meyers (Ed.), Handbook of Petroleum Refining Processes, New York, San Francisco, Washington, D.C., Auckland, Bogota, Caracas, Lisbon, London, Madrid, Mexico City, Milan, Montreal, New Delhi, San Juan, Singapore, Sydney, Tokyo, Toronto: McGraw-Hill, 1996, 11.3). Another method is the UOP Merox process. In this process, the mercaptans present in the fuel are reacted with oxygen to form disulfides in the presence of an organometallic catalyst at low temperatures in an alkaline medium (D. L. Holbrook, UOP Merox Process, in: R. A. Meyers (Ed.), Handbook of Petroleum Refining Processes, New York, San Francisco, Washington, D.C., Auckland, Bogota, Caracas, Lisbon, London, Madrid, Mexico City, Milan, Montreal, New Delhi, San Juan, Singapore, Sydney, Tokyo, Toronto: McGraw-Hill, 1996, 11.29).
Halogenated impurities in hydrocarbons and mixtures of hydrocarbons cause corrosion problems in engineering, and therefore, their content must usually be reduced down to a range of a few ppm. This can be achieved by catalytic hydrogenation or electrolytic dehalogenation (G. Scharfe, R.-E. Wilhelms (Bayer Aktiengesellschaft), U.S. Pat. No. 3,892,818 (1975), J. Langhoff, A. Jankowski, K.-D. Dohms (Ruhrkohle A G), U.S. Pat. No. 5,015,457 (1991), W. Dohler, R. Holighaus, K. Niemann (Veba Oel Aktiengesellschaft), U.S. Pat. No. 4,810,365 (1989), F. F. Oricchio (The Badger Company, Inc.), U.S. Pat. No. 3,855,347 (1974), R. W. La Hue, C. B. Hogg (Catalysts and Chemicals, Inc.), U.S. Pat. No. 3,935,295 (1976), F. Rasouli, E. K. Krug (ElectroCom Gard, Ltd.), U.S. Pat. No. 5,332,496 (1994), H. J. Byker (PCB Sandpiper, Inc.), U.S. Pat. No. 4,659,443 (1987), J. A. F. Kitchens (Atlantic Research Corporation), U.S. Pat. No. 4,144,152 (1979)). However, catalytic hydrogenation is not desirable on a large scale and there is a need for efficient yet more cost effective processes to remove halogenated impurities from hydrocarbons.
Ionic liquids have been known for many years (P. Wasserscheid, W. Keim, Angew. Chem., 112 (2000) 3926; T. Welton, Chem. Rev., 99 (1999) 2071; J. D. Holbrey, K. R. Seddon, Clean Products and Processes, 1 (1999), 223). They are characterized by being liquids that consist exclusively, or substantially exclusively, of ions. Important properties include their solubility properties, which can be adjusted within wide limits by varying the cation and/or anion, and their extremely low vapor pressure. Numerous ionic liquids are not completely miscible with hydrocarbons and mixtures of hydrocarbons, i.e., the formation of two-phase or multi-phase systems occurs (P. Wasserscheid, W. Keim, Angew. Chem., 112 (2000) 3926).
In view of the above, there is an immediate need for efficient and costs effective processes for the removal of impurities, such as polar or polarizable impurities, from useful hydrocarbons or hydrocarbon mixtures.